SUN-213 The Role of Filamin A (FLNA) in the Regulation of Insulin-Like Growth Factor System in Adrenocortical Carcinomas

Abstract Adrenocortical carcinomas (ACCs) are rare endocrine tumors with poor prognosis. They overexpress insulin-like growth factor 2 (IGF2), that drives a proliferative autocrine loop by binding to IGF1R and IR, with molecular dynamics still poorly identified. Although promising, IGF1R/IR-targeted therapies have demonstrated a limited efficacy in clinical trials in ACC patients. The cytoskeleton actin-binding protein filamin A (FLNA) was shown to impair IR and IGF1R signalling in melanoma and neural progenitor cells, respectively. The aims of this study were to test in ACC cells: 1) FLNA involvement in regulating IGF1R and IR expression and signalling; 2) FLNA role in modulating responsiveness to IGF1R and IGFR/IR inhibitors; 3) FLNA expression in ACCs and correlation with IGF system. In ACC cells we found by immunoprecipitation that both IGF1R and IR interacted with FLNA in basal condition, with an increased or decreased FLNA recruitment to IGF1R and to IR, respectively, after IGF2 stimulation. Genetic silencing of FLNA in ACC cell lines H295R and SW13 induced a significant increase of IGF1R expression (1.4- and 2.3-fold, respectively) and a reduction of IR (-85.5±9.1%, p<0.001 and -32±19.1%, respectively, p<0.05), with a downstream effect of increased cell proliferation (130±13.4%, p<0.01 in H295R and 144.3±23.3%, p<0.01 in SW13 cells) accompanied by an enhanced ERK phosphorylation. Accordingly, in ACC primary cultured cells FLNA silencing increased IGF1R levels (2.9-fold) and enhanced IGF2 effects on ERK phosphorylation by 2.2-fold. In addition, FLNA knockdown potentiated the antiproliferative effects of IGF1R/IR inhibitor Linsitinib and IGF1R specific inhibitor NVP-ADW742 in H295R cells and SW13. This key role of FLNA was even more evident in A7/M2 melanoma cell model, since IGF2 and Linsitinib exerted the expected effects on ERK phosphorylation in M2 cells, lacking FLNA, but not in FLNA-expressing counterpart (A7 cells). Finally, western blot analysis showed significantly lower, although variable, FLNA expression in ACCs (n=10) than in adrenocortical adenomas (ACAs) (n=10) (FLNA/GAPDH ratio 0.37±0.38 and 0.90±0.63, respectively, p<0.05). Interestingly, FLNA/IGF1R ratio inversely correlated with ERK phosphorylation status in ACCs (p<0.05) but not in ACA. In conclusion, we demonstrated that low levels of FLNA enhance both IGF2 proliferative effects and IGF1R/IR inhibitors efficacy in ACC cells, suggesting FLNA as a new factor possibly influencing tumor clinical behavior and the response to the therapy with IGF1R/IR-targeted drugs.